We strongly recommend you to zip all files for a board to an archive file. This simplifies handling for us, and also makes it a lot safer and faster.
On the page "Technology classes" under "Space, inner – outer layer" you will find the most commonly used distances.
It is optimal, if possible to have the Cu surface evenly distributed over the entire board. It can be risky to design for example a 4-layer board where layer 3 is a ground plane and layer 2 is a signal layer with almost no Cu around lines. This design can make the board bend in production or when soldered.
It is good practice to mark the layers in the Cu like 1,2,3,4 etc. or L1,L2 etc.